A water-granulated blast furnace slag (hereinafter referred to as a "water-granulated slag") used as a raw material for cement has conventionally been manufactured by spraying pressurized cooling water to a molten slag discharged from a blast furnace. Since the molten blast furnace slag is cooled and solidified through contact with the cooling water, the water-granulated slag thus obtained is vitrified. A water-granulated slag is usually applied as follows:
However, because a water-granulated slag, coming into direct contact with a cooling water in the course of manufacturing, usually contains about 15 wt.% water. To apply a water-granulated slag for any of the uses mentioned in (a) through (d), it is necessary to dry the water-granulated slag in advance. This drying requires about 17 liters heavy oil per ton of water-granulated slag, and in addition, transportation cost for the unnecessary water content is required when transporting the water-granulated slag before drying. For the uses (b) and (c) above, furthermore, it is necessary to finely pulverize the water-granulated slag previously until the specific surface area value based on the Blaine-air-permeability method (hereinafter referred to as the "Blaine fineness") reaches from about 3,000 to about 4,000 cm.sup.2 /g, thus requiring from about 60 to about 100 KWH electric power per ton of water-granulated slag. During the manufacture of the water-granulated slag, contact with the cooling water leads to the production of such noxious gases as hydrogen sulfide gas, resulting in worsening working environments, and moreover, soluble substances useful for a cement contained in the slag such as lime, silica and alumina are lost by dissolution into the cooling water.
With these facts in view, the following granulating process and granulating apparatus of a molten blast furnace slag have been proposed.
feeding a molten material such as a molten steel and a molten slag onto a rotary disk in rotation; granulating said molten material by causing said molten material to scatter under the effect of centrifugal force produced by the rotation of said disk; covering the periphery of said disk with a frustoconical casing flaring downwardly; forming a film of cooling water flowing downwardly along the inner surface of said casing; and, cooling and solidifying said granulated molten material by the contact with said film of cooling water (hereinafter referred to as the "prior art (1)").
feeding a molten slag into a rotating rotary drum inclined by 2.degree. to 20.degree. relative to the horizontal line from an inlet on the higher side thereof, while cooling the barrel of said drum by spraying cooling water onto the outer surface of said drum; cooling and solidifying said molten slag by the contact with the inner surface of said drum, and at the same time, crushing said solidified slag by the rotation of said drum; and, discharging said crushed slag from an outlet on the lower side of said drum (hereinafter referred to as the "prior art (2)").
feeding a molten slag onto the outer surface of a rotating rotary drum; granulating said molten slag by causing same to scatter in front of said drum under the effect of centrifugal force produced by the rotation of said drum; and, cooling and solidifying said granulated molten slag by a cooling system installed within the scattering area of said granulated molten slag (hereinafter referred to as the "prior art (3)").
vitrifying a molten blast furnace slag by granulating, while cooling and solidifying, said molten blast furnace slag by blowing the molten blast furnace slag with a pressurized fluid such as a pressurized air and a pressurized steam, or by causing the molten blast furnace slag fed onto a rotating rotary disk to scatter under the effect of centrifugal force produced by the rotation of said rotary disk; and, finely pulverizing said vitrified granulated blast furnace slag (hereinafter referred to as the "prior art (4)").
However, in any of the above-mentioned prior arts (1) to (4), partial crystallization of molten blast furnace slag is inevitable, because it is impossible to obtain a high cooling rate sufficient to completely vitrify the molten blast furnace slag. In the prior arts (1) and (3), furthermore, problems similar to those in the water-granulated slag mentioned above are encountered, since water is still employed as the cooling medium.
With a view to solving these problems, there has been proposed, in Japanese Patent Application No. 126,098/78 dated Oct. 16, 1978, an apparatus for manufacturing a vitreous blast furnace slag, which comprises:
a rotary drum having a substantially circular barrel formed by endlessly connecting a plurality of rectangular cooling metal members, each of said plurality of cooling metal members having on the outer surface thereof a plurality of narrow and deep cooling grooves with the longitudinal direction substantially in parallel with the rotating direction of said rotary drum, and each of said plurality of cooling grooves comprising an outwardly flaring inlet section for introducing a molten blast furance slag and an inwardly narrowing cooling section, following said inlet section, for rapidly cooling and solidifying the molten blast furnace slag into a vitreous blast furnace slag;
a driving mechanism, connected to the center axle of said rotary drum, for rotating said rotary drum;
a molten blast furnace slag feeder including a slag container, arranged above said rotary drum, said molten blast furnace slag feeder being adapted to receive a molten blast furnace slag discharged from a blast furnace into said slag container and pour said molten blast furnace slag thus received into said plurality of cooling grooves of said cooling metal member reaching about the highest position of the barrel of said rotary drum along with the rotation of said rotary drum;
a stripper stationarily arranged at a prescribed position in said rotary drum adjacent to the inner surface of the barrel of said rotary drum, said stripper being adapted to take out a cooled and solidified vitreous blast furnace slag in said plurality of cooling grooves of said cooling metal member; and,
a cooling tank containing cooling water, arranged below said rotary drum so that the lower portion of the barrel of said rotary drum is immersed in the cooling water, said cooling tank being adapted to cause said plurality of cooling metal members forming the barrel of said rotary drum to successively pass through the cooling water in said cooling tank along with the rotation of said rotary drum, thereby cooling said cooling metal members heated by the high-temperature molten blast furnace slag poured into said cooling grooves (hereinafter referred to as the "earlier invention").
The aforementioned apparatus for manufacturing a vitreous blast furnace slag (hereinafter referred to as the "apparatus of the earlier invention") has a high cooling rate sufficient to substantially completely vitrify a molten blast furnace slag, and furthermore, the molten blast furnace slag is cooled rapidly and solidified by the direct contact with the cooling metal members, instead of the direct contact with cooling water. According to the apparatus of the earlier invention, therefore, it is possible to manufacture a vitreous blast furnace slag which is substantially completely vitrified, substantially free of water, excellent in grindability, and has a high quality as a raw material for a cement or for a calcium silicate fertilizer. In the earlier invention, however, a plurality of cooling metal members form the substantially circular barrel of the rotary drum. In the apparatus of the earlier invention, therefore, in order to improve the production capacity, it is necessary to use wider cooling metal members to increase the number of cooling grooves, or to use a rotary drum with a larger diameter to increase the number of cooling metal members. However, with wider cooling metal members comprising a larger number of cooling grooves, it becomes difficult to uniformly pour a molten blast furnace slag into the cooling groovs. With more cooling metal members with a larger-diameter rotary drum, it is necessary to ensure a sufficient head between the slag container and the cooling metal members by providing a pit in the ground and accommodating the lower portion of the rotary drum in this pit, thus requiring higher installation costs.